Method of making magnetic cores



Oct. 1l, -1960 G. J. MAxsoN 956,024 METHOD OF' MAKING MAGNETIC CORESFiled April 1, 1957l v @Sk SSNQ l/ ,mfhq

Manganese 16.34 Carbonate 44.93,-

ing weights of the constituent metals in accordance with the abovepercentages.

It is yet another object of this invention to produce manganese zincferrites which will exhibit values of u and Q that provide a productwell in excess of 100,000 when subjected at room temperature (70 to 95 eF.) to a maximum flux density of ygausses varying at a frequencyof .100kilocycles. y

United States Patent O Patented Oct. 1l, 1960 With the foregoing andother objects in mind, the in'- vention is directed primarily to methodsof producing a 2956 024 manganese zinc ferrite article having a ,LQproduct'in excess of 100,000 when subjected to a flux density of 5METHOD 0F MAKING MAGNETIC CORES 5 gausses at a frequency of 100kilocycles. A method, i1- Gordon J Maxson Downers Grove nl asignor tolustrating certain features of the invention, may include WesternElectric Company Incomrate, New York, the steps of forming an mtunatemixture of 23.8 percent N Y', a corporation of New York MnCO3 by we1ght,14.4 percent ZnO, and 61.8 percent Fe203, adding a chlorinatednaphthalene bmder, and Filed Apr. 1, 1957, Ser. No. 650,049 forming acompressed article from the mixture. The article thus formed is thenheat treated according to a 2 Clmms (CL 252-625) schedule including thesteps of (1) heating the article to volatilize the binder, (2) withoutappreciable temperature drop after the volatilization step sintering thearticle This invention relates to a method of making magnetic at atemperature of about 2170 F. in la protective atcores, and moreparticularly to a method of making mosphere consisting of 99.25 percentnitrogen and 0.75 manganese zinc ferrite cores. percent oxygen, (3)reducing the temperature of the ar- Ferromagnetic oxide compounds,commonly called ferticle i0 about 180 F- at a maximum rate Of 350 F-rites, have come into wide use in the past -few years in per hour, (4)quenching said `article to a temperature of the making of cores forinductance coils, radio freof about 1000 F. within about 5 minutes witha cool quency transformers, and various other applications. Supply 0fSaid prcecivc atmosphere, and (5) Slowly Ferrites are made by sinteringiron oxide with one or Cooling said article to room temperature with anaddimore oxides or carbonates of bivalent metals to produce tionalSupply 0f Said atmcSPherea Crystalline material having magneticproperties. To Other objects, advantages and novel features of theproduce materials having good magnetic properties, the invention willbecome vapparent upon consideration of ingredients must be meticulouslyprepared and red. It rthe fOllOWIlg detailed description in CODJ'UIICOIIWith has been found that the selection and preparation of the theaccmParlYlIlg drawings wherein: constituents alone does not completelycontrol the mag- Fig. 1 is a side elevation View of a heat zoned tunnelnetic properties of the final product; the rin-g process YPe furnaceused in Practicing the invention; is also of critical importance. Forexample, a tiring time Fig- 2 iS a temperature VS- ime graph I0f thedcWaXing which is too short will result in a low permeability (a) andfiring Process? and whereas a firing time which is too long will resultin a Fi'g- 3 S a graph 0f Q factor VS- Percent 0f Oxygen low Q factor.present in the protective atmosphere during the tiring It has beendetermined that manganese zinc fcrrites, Operation; when properlyprepared and red, exhibit very high per- An actual procedure that wasutilized for producing meability and Q factor values, and consequently,a very magnetic bodies having the above-described constituents high ,uQproduct. Experiments have demonstrated that and magnetic Properties Was21S fcllcWS Three lOSOf the composition 0f a manganese zinc ferritewhich exraw materials consisting respectively of iron oxide, zinc hibitsthe optimum values Vof the ,aQ product is one in oxide, `and manganesecarbonate, all of reagent grade, which the three metallic elements arepresent in the final 40 were assayed and the following compositions werefound: illpgxenzcll 1n the followmg percentages by weight of theCompound: Percentmetal Percent Fe203 69.86 Iron 66.10 VZnO 1 79.53Manganese 16.34 MnCOa 44.93 Zmc 17'56 45 The next step was to obtain theratio of the percentage It is therefore an object of this invention toprovide a by weight of Itotal metal desired for each element to theprocess which will produce ferrites having a high ,MQ percentage byweight of total 4metal as obtained for each product. raw materialthrough the chemical analysis. The quo- It is another object of thisinvention to provide a irtients of these ratios for the three lelementswere then ing process which will produce manganese zinc ferrites addedand each quotient divided by the total. Therehaving very highpermeability (,u) and Q factor values. sulting percentages were thenmultiplied -by the size of It is another object of this invention toprovide a procmix desi-red to obtain individual weights of rawmaterialsV ess which will produce manganese zinc ferrites containto beused. These calculations are shown below. i

Iron 66.10 Y Oxide m- .947-.-1.531 -61.8%X40 lb. mix- 24.74 lb.

Zinc 17.56 Oxide m- .220-.-.1.531 100- 14.4%X40 lb. mix-5.76 lb.

.Stiller-1.531 XV100= 273.8%X 40113. mix= 9.50113.

'Ifhe'raw materials were then weighed out in accordance with thecalculated proportions and mixed with -wa at 350 F. for 4 hours and thengranulated by meansv of a granulatorutilizing an agitator and ainchfmesh` screen. :The-granules'were' thenloaded into quartz -sag-`gers and placed in a preliminary ring or calcining furnace which waspreheated to a temperature of 1750" F. After 4 hours in the furnace, thesaggers were removed and air cooled. This step causes most of thevshrinkage, which the materials will undergo, to take. placeandralsoreduces the MnCO3 to MnO and. CO2 which passes off as `a gas. Also, thechemical reaction between theA raw materials is partially completed andsome ferrite is formed.

The calcined powder was next mixed with carbon tetrachloride and Halowax(a chlorinated naphthalene) and ground in a ball mill for 22 hours. TheCClrwas added to provide a liquid vehiclefora wet grinding operation andthenthe Halowax was added and thoroughly mixed with the powder in orderto serve asiaV binder in a subsequent pressing operation. The CCl4 wasthen removed by fractional distillation leaving the powder impregnatedwith the Halowax The lumps of powder resulting from the previous stepwere then reduced in a granulator using l/fs inch mesh screens and thenaged for l days at room temperature. The powder was then pressed intoappropriately shaped articles using tungsten, carbide dies and apressure of 25 tons/m2. The articles were then ready to be dewaxed.

Referring now -to the drawings, there can be seen a furnace (Fig. l)formed of three sections, namely, dewaxing, firing and cooling sectionsdenoted by the reference letters A, B and C. In using this furnace thepreviously pressed articles are loaded into mullite (aluminum silicate)saggers and the saggers in turn are placed in the left hand end (Fig. 1)of the dewaxing section at spaced intervals. A solenoid valve (notshown) is then energized to actuate a pneumatic cylinder 11 to cause thesaggers 10 within `the dewaxing section to be moved to the right. Whensufficient saggers `are present in the dewaxing section, the one on theright hand end trips a limit switch 12 which energizes a solenoid valve(not shown) to actuate pneumatic cylinders 13 and 14 which lowerplatforms 15 and 16 to the positions shown by4 dotted lines. Platform 15trips limit switch 18 to actuate cylinder 19 which in turn pushes theloaded sagger 10 onto platform 16 in the position designated by` thenumeral 10". When the sagger reaches the position 10, limit switch 20 istripped causing cylinder 14 to elevate platform 16 to the position shownin solid lines; at which point the saggerenters the firing-section BV ofthe furnace.

Asplatformv 16'isbeing elevated; it trips limit switch 21' to actuatecylinder 22 which pushes the` sagger or saggers, within the firingsection B, to the right (Fig. 1). When the firing section is loaded, theadvance of the right hand sagger will trip limit switch 24 each timecylinder 22 is actuated. Switch 24 functions to actuate cylinder 25which lowers platform 26 to trip limit switch 27. Switch 27 then causescylinder 29 to pusha sagger 10 resting on platform 26 into the coolingsection C of 'the furnace. The loaded saggers progress through thecooling section of the furnace, as a result of the cooperation'ofcylinders 29, 30 and 31 and limit switches 33 and 34, in the same manneras that in which they passed throughfthe firing section and areeventually deposited upon bench 36 when sufficiently cooled. It isobvious, of course, that cylinders 11, 22, 29 and 31 must'allfunctionsuccessivelyV at the same frequency.

Returning now to the actual procedurewhich was utilized to produceferrite articles, there can be seen in Fig. 2 a temperature vs. timegraph of thejdewaxing, firing and cooling cycle used in preparingferrites according to the invention. The saggers containing the pressedarticles were subjected to a. temperature of 200 F. im. mediately uponbeing placed in the lefthand end of the.

dewaxing section A. The temperatures of theI various:

zones of the dewaxing section, the frequency Vofintroduction ofadditional saggers and the length of the dewaxing section werepredetermined so as. to subject'ithepressedl articles `to a temperaturerise of approximately 150 and to then maintain the articles at 900 F.for approximately 4 hours. An exhaust system (not shown) was provided tocontinuously change the air atmosphere within the dewaxing section inorder to carry off the volatilized binder (Halowax). Upon completion ofthis heating cycle, the saggers were then periodically transfered to thefiring section B of the furnace. The transfers were rapidly effected toinsure a minimum drop of temperature of the articles.

The Ileft hand zone of the firing section B was maintained at 1000 F. inorder to begin heating thearticles still further upon their introductioninto the firing section. The zone temperatures, indexing. frequency andlength of the firing section were predetermined so as to provide thefollowing firing cycle, (l) a gradual temperature rise from 1000 F. to2170 F. at a rate of approximately 350 F./hr., (2) a constant firingtemperature of 2170 F. for 6 hours, and (3) a gradual cooling from 2170"F. to l800 F. at the rate of approximately 350 F./hr. A continuouslychanging protective atmospherewas maint-ained in the firing sectionconsisting of 99.5% to 99.25% nitrogen with the remainder being oxygen.It was experi- I mentally determined that the amount of oxygen presentin the atmosphere surrounding the articles being fired had a` decidedeffect on the Q factor of the completed articles (Fig. 3), i.e. a higheror lower percentage of oxygen present would drastically lower the Qfactor. An oxygen content of approximately 0.75% was found to produceoptimum results.

After cooling from the firing temperature of 2170o F. to 1800 F., thesaggers were transferred to the cooling section C of the furnace wherethey were subjected to a cool protective atmosphere of theabove-described composition which quenched the articles and reducedtheir temperature from 1800 F. to 1000 F. in about 5 minutes. Thepurpose of this rapid quench was to preserve the magnetic properties ofthe finished articles since it was found that permitting the articles tocool slowly resulted in very low and unsatisfactory values of ,u and Q.

The articles were then more slowly cooled to a temperature at which theycould be safely handled and were then ejected from the cooling section.When the articles made in accordance with the described process weresubjected toa flux `densityof 5 gausses at a frequency of kilocycles,the articles exhibited values of permeability (a) and Q factor whichyielded a #Q product averaging-150,000.

There have Ythusrbeen described improved ferrite' materials exhibiting'unexpected improvements in several of their useful magnetic properties.The proportions of the ingredients used and the firing steps describedshould, in general, be closely adhered to since substantial variationswill yield products which are either not significantly irnproved or areinferior to previously ltnown` ferrites.

It-is to be understood however that the above described method issimply'illustrative of an application of the principles of the inventionand that modifications can be made without departing from the invention.

What is claimed is:

l. A method of producing a manganese zinc ferrite article having a ,uQproduct in excess of 100,000 when subjected to a flux density of 5gausses at a frequency of 100 kilocycles which comprises the steps offorming an intimate mixture of 23.8 percent MnCO3 by weight, 14.4percent ZnO, and 61.8 percent Fe203, adding a chlorinated naphthalenebinder, forming a compressed article from said mixture, heating saidalticle to volatilize said binder, without appreciable temperature dropafter the volatilization step sintering said article at a temperature ofabout 2170" F. in a protective atmosphere consisting of 99.25 percentnitrogen and 0.75 percent oxygen, reducing `the temperature of saidarticle to about `1800e F. at a maximurn rate of 350 F. per hour,`quenching'said article to aitemperature of about 1G00 F. within about 5minutes with a cool supply of said protective atmosphere, and

'l il slowly cooling said article to room temperature with an additionalsupply of said atmosphere.

2. A method of producing a manganese zinc ferrite article exhibiting a#Q product characteristic in excess of 100,000 when subject to a Iliuxdensity of 5 gausses at a frequency of 100 kilocycles which comprisesthe steps of forming an intimate mixture of 23.8 percent v MnCO3, 14.4percent ZnO, and 61.8 percent Fe203, all

of said percentages being by weight, adding a chlorinated naphthalenebinder, forming a compressed article from said mixture, heating saidarticle to a temperature of about 900 F. at a maximum rate of 150 perhour, maintaining said article at about 900 F. for approximately 4 hoursto volatilize and drive off said binder, increasing the temperature ofsaid article to about 2170 F. at a maximum rate of 350 F. per hour whilemaintaining a protective atmosphere about said article which consists of99.25 percent nitrogen and 0.75 percent oxygen, the lastmentionedheating step being performed immediately after the volatilization stepso that there is no appreciable 2 temperature drop below 900 F.,sintering said article at about 2170 F. for approximately 6 hours whilecontinuing to supply said protective atmosphere, reducing the 6temperature of said article to about 1800 F. at a maximum rate of 350per hour, quenching said article to a temperature of approximately 1000"F. within a period of about 5 minutes with a cool supply of saidprotective atmosphere, and slowly cooling said article to roomtemperature with an additional supply of said atmosphere.

References Cited in the le of this patent UNITED STATES PATENTS2,723,238 Simpkiss Nov. 8, 1955 2,764,552 Buckley et al. Sept. 25, 1956FOREIGN PATENTS 669,571 Great Britain Apr. 2, 1952 730,703 Great BritainMay 25, 1955 1,056,511 France Oct. 21, 1953 OTHER REFERENCES NewDevelopments in Ferromagnetic Materials, by Snoek, Elsevier Pub. Co.,1947, pp. 91 and 92.

Proceedings of the IRE, vol. 44, No. 10, October 1956, pp. 1304, 1305and.1307.

1. A METHOD OF PRODUCING A MANGANESE ZINC FERRITE ARTICLE HAVING A $QPRODUCT IN EXCESS OF 100,000 WHEN SUBJECTED TO A FLUX DENSITY OF 5GAUSSES AT A FREQUENCY OF 100 KILOCYCLES WHICH COMPRISES THE STEPS OFFORMING AN INTIMATE MIXTURE OF 23.8 PERCENT MNCO3 BY WEIGHT, 14.4PERCENT ZNO, AND 61.8 PERCENT FE2O3 ADDING A CHLORINATED NAPHTHALENEBINDER, FORMING A COMPRESSED ARTICLE FROM SAID MIXTURE, HEATING SAIDARTICLE TO VOLATILIZE SAID BINDER WITHOUT APPRECIABLE TEMPERATURE DROPAFTER THE VOLATILIZATION STEP SINTERING SAID ARTICLE AT A TEMPERATURE OFABOUT 2170*F. IN A PROTECTIVE ATMOSPHERE CONSISTING OF 99.25 PERCENTNITROGEN AND 0.75 PERCENT OXYGEN, REDUCING THE TEMPERATURE OF SAIDARTICLE TO ABOUT 1800*F. AT A MAXIMUM RATE OF 350*F. PER HOUR, QUENCHINGSAID ARTICLE TO A TEMPERATURE OF ABOUT 1000*F. WITHIN ABOUT 5 MINUTESWITH A COOL SUPPLY OF SAID PROTECTIVE ATMOSPHERE, AND SLOWLY COOLINGSAID ARTICLE TO ROOM TEMPERATURE WITH AN ADDITIONAL SUPLY OF SAIDATMOSPHERE.